We examined the effect of ultraviolet (UV) irradiation on the expression of
cyclooxygenases in cultured HaCaT keratinocytes and in human skin in vivo.
UVB irradiation (10 and 50 mJ/cm(2)) and hydrogen peroxide (200 mu mol/L)
increased cyclooxygenase-2 mRNA expression in HaCaT keratinocytes. No clear
expression of cyclooxygenase-1 mRNA was detected in either control or stim
ulated HaCaT cells. Genistein, a tyrosine kinase inhibitor, suppressed both
the basal and stimulated expression of cyclooxygenase-2 in HaCaT cells. UV
B-induced cyclooxygenase-2 mRNA expression was partly inhibited by the anti
oxidant N-acetylcysteine and by H-7, a non-specific inhibitor of protein ki
nase C. Solar-simulated irradiation (40 mJ/cm(2)) was found to induce in vi
vo both cyclooxygenase-2 mRNA and protein expression in human skin, whereas
the expression of cyclooxygenase-1 mRNA remained at the basal level. Our r
esults show that cyclooxygenase-2 expression is induced by UV irradiation a
nd suggest that tyrosine kinases and reactive oxygen intermediates are invo
lved in this induction of cyclooxygenase-2.